When using a photometer it is important to insert the cuvette in the same position when performing a blank measurement (zero) and a read with reacted sample in order to maintain a consistent path length in accordance with the Beer-Lambert Law (see below). The HI731335 have a locking index tab in the cap that fits with the HI96 series photometers to ensure that the cuvette is inserted in the same orientation each time.

The quantity of radiation absorbed is given by the Beer-Lambert Law:

A = log( I_o / I )

Absorbance is also given by: A= ελ • C • l where:

A is a dimensionless number

ελ the proportionality constant, is called the molar extinction coefficient or molar absorptivity; it is a constant for a given substance, provided the temperature and wavelength are constant [L/(mol•cm)]

C is the concentration of the substance (mol/liter)

l is theoptical distance light travels through sample (cm)

The HI731335 are the replacement caps for glass cuvettes that are supplied with all HI96 series portable photometers. The are also designed to keep any stray light from entering the sample cuvette holder of the optically based system.